To date, acrylic materials having a frosted or matt appearance have always been obtained from PMMA, which PMMA may be slightly modified:                either by introduction of impact modifiers having a flexible core/rigid shell structure;        or by incorporation of comonomers, such as, for example, acrylates, which make it possible to improve the thermal stability, or acrylic or methacrylic acids, which make it possible to improve the temperature stability.        
The document EP 1 022 115 describes extruded polymer articles having a matt appearance and a textured finish, comprising a PMMA-based matrix and highly crosslinked MMA-based polymer particles.
The document EP 2 089 473 describes the preparation of methacrylic compositions comprising an MMA homo- or copolymer in which particles of crosslinked MMA-based thermoplastic polymers are dispersed.
These materials are manufactured by dispersing crosslinked acrylic beads in a PMMA matrix in the molten state (compounding). The materials obtained scatter light while allowing it to pass (for example, shower stalls having a frosted appearance). They are also highly resistant to UV radiation. However, these materials have the disadvantage of being very rigid and of having a poor impact strength. Furthermore, the size of the crosslinked acrylic, beads directly influences the roughness of the final product.
The development of acrylic materials in the field of optical waveguides or of the coating of other materials is thus limited by the stiffness and brittleness of current materials.
It is therefore desirable to introduce novel properties to low-gloss acrylic materials by improving their impact strength or by manufacturing even “flexible” acrylic materials. This type of material can offer novel applications, for example in the field of design (illuminations) and coatings of materials.
To this end, a subject matter of the present invention, according to a first aspect, is a semirigid or flexible acrylic material comprising:                a nanostructured matrix composed of at least one thermoplastic acrylic block copolymer,        and at least one highly crosslinked acrylic copolymer.        
This combination has the effect of resulting in a material which exhibits a group of novel properties since the material is simultaneously flexible, highly impact resistant, non glossy and resistant to UV radiation and has a surface which, unexpectedly, once processed, has a soft touch which is very pleasant and more or less pronounced according to the blend produced between a soft material (the nanostructured matrix) and another very hard material (the highly crosslinked acrylic copolymer).
These materials can be transformed by injection molding, extrusion, coextrusion or extrusion/blow molding for the preparation of parts, profiled elements, sheets or films, for example.
The product can advantageously be used as coating on other materials. For example, use may be made of the technique of coextrusion or lamination of film on a substrate. It is also possible to produce profiled elements which can be used, for example, in optical applications.
It is also possible to manufacture multilayer structures comprising a first layer consisting of the acrylic material according to the invention and a second layer comprising at least one substrate made of a thermoplastic polymer material.
The invention will now be described in detail.
The development of anionic polymerization and of controlled radical polymerization made it possible, towards the start of the 1990s, to synthesize acrylic block copolymers, for example diblocks of polymethyl methacrylate-polybutyl acrylate (PMMA-pBuA) or polymethyl methacrylate-polybutadiene type, or also triblocks of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate or polystyrene-polybutadiene-polymethyl methacrylate type.
In comparison with random copolymers, block copolymers make it possible to obtain novel morphologies, with in particular organizations in domains of a few nanometers of the various phases formed by each of the blocks. These organizations are, for example, described in Macromolecules, Vol. 13, No. 6, 1980, pp. 1602-1617, or also in Macromolecules, vol. 39, No. 17, 2006, pp. 5804-5814. This type of organization is referred to as “nanostructured”.